Summary: Currently, enhanced inactivated poliovirus vaccine (eIPV) are produced using wild-type poliovirus strains as substrates. The strains possess high pathogenic potential and if they were to be accidentally released from manufacturing areas into communities (and such an accident has actually occurred) they might be responsible for outbreaks of poliomyelitis. After eradication of poliomyelitis is completed, work with wild-type polioviruses will require strict containment measures, which will demand serious changes in the manufacturing process to protect surrounding communities, and to prevent potentially catastrophic consequences of poliovirus release. An attractive alternative approach to safety of eIPV production would be to switch to using non-pathogenic strains of poliovirus. During previous years of the project we have studied neurovirulene of genetically engineered strains proposed for produciton of IPV. We have found that some of them retained significantt genetic instability making them inapproapriate for production of vaccine. Now we focused our studies on development of new approaches to evaluation of immunogenicity and efficacy of IPV produced from attenuated Sabin strains (sIPV). We have shown that type 2 IPV produced from Sabin strain is less immunogenic than the conventional IPV made from MEF-1 strain. There was poor correlation between antibody levels and protection against lethal challenge with poliovirus as determined in Tg-mouse test. We are now focusing on determining an epitope profile of both conventional and sIPV.